FF, Just a small point but the "approach ban" preventing you from descending below 1000' aal only applies to the RVR and not to the cloudbase. It is still legal to make an approach if the reported cloudbase is below the DA or MDA (actually DH or MDH) but not if the RVR is below the required figure for the particular approach.
My reading of the 800 RVR limit for single-pilot operations is that it only applies to public transport flights. However, the CAA have said in the past couple of years that it applies to all flights. How this can change without a change to the ANO is beyond me. It is also odd in that most single-pilot approaches are made in cat A aircraft with a much lower threshold speed than most public transport approaches.
RR, I have a feeling that the 1800m RVR is a licence restriction for IMC holders rather than anything else. My ANO says that a PPL without any ratings must have a min visibility of 3km (outside controlled airspace).